This invention relates to an improved apparatus for monitoring and controlling liquid levels. More particularly, the invention relates to such an apparatus which involves magnetically-operated switches as an integral part thereof.
The monitoring and control of liquid levels in various receptacles or containers, i.e., storage tanks, is clearly important in many instances in many industries. The use of magnetically operated switches to monitor liquid levels has been suggested for example, in U.S. Pat. Nos. 3,548,659 and 3,982,087. Such previous devices have merely served to indicate the level of liquid in a container. Controlling the level of liquid in a storage tank may be of vital importance to avoid dangerous, and even deadly, conditions.
Therefore, one object of the present invention is to provide an apparatus for controlling the liquid level in a storage tank.
Another object of the present invention is to provide an apparatus for monitoring the liquid level in a storage tank.
A still further object of the present invention is to provide an apparatus for monitoring and controlling the liquid level in a storage tank, which apparatus involves magnetically operated switches. Other objects and advantages of the present invention will become apparent hereinafter.
An improved apparatus for monitoring and controlling the level of liquid in a storage tank equipped with a pump to discharge liquid, as desired, has now been discovered. The apparatus includes a tubular guide extending substantially vertically inside the storage tank with first and second magnetically operated (or activated) switches located therein. The second switch is located a distance above the first switch. A first electrical current source causes current to pass through the first and/or second switch when the first and/or second switch is in the closed position and forms part of an electrical circuit.
Further, the apparatus includes a float which is slidable on the exterior of the guide in response to the level of liquid, the float carries a magnet having sufficient force to activate the first and second switches as the float slides on the guide to a location in proximity to one or the other of such switches. The term "activate" as used in reference to the presently useful magnetically operated switches means that the switch is caused to move from its normal mode. Thus, a normally closed first switch is activated by the magnet in the float to an open position.
A second electrical current source is included to provide current to activate the discharge pump in response to the position of the first and second switches. Although the pump is preferably electrically driven, it need not be and may be chosen based on the type of liquid being handled and the conditions of handling. For example, current from the second current source may open valving arrangements to allow steam or compressed air to run a pneumatically driven pump. In any event, the pump is electrically activated, directly or indirectly. A first relay, in communication with the first and second switches allows current from the second source to start flowing to activate the pump as the magnet activates the second switch. Once current to the pump starts flowing, such current is interrupted in response to the magnet activating the first switch.
The present apparatus is seen to effectively control the level of liquid in the storage tank, e.g., between the levels corresponding to the locations of the first and second magnetically operated switches.
In a preferred embodiment, the present apparatus further includes an alternate second magnetically operated switch which is located in the tubular guide a distance above the second magnetically operated switch. This alternate switch is also in electrical communication with the first current source so that current passes through this alternate switch when it is in the closed position and part of an electrical circuit. Current from the second current source will start flowing to the pump (if the current is not already flowing) as the magnet in the float activates the alternate switch. Only one of the second switch or the second alternate switch need be activated, e.g., by the magnet in the float, to start current flowing to the pump. Thus, the alternate second magnetically operated switch provides substantial safety benefits to the present apparatus. If for some reason, e.g., an electrical power failure, the second switch is not activated as the magnet in the float passes by this second switch, the magnet has a "second" charge to activate the discharge pump by activating the alternate second switch located at a higher level. In a still further preferred embodiment, the tubular guide includes a top block to prevent the float from rising any higher in the storage tank. The top block is preferably positioned so that as the float contacts the top block, the magnet in the float is in position to activate the alternate second switch. For example, when the electrical power is turned back on, current will immediately start flowing to the pump regardless of how far above the second alternate switch the liquid level is. The use of a top block as described above represents an additional safety feature of the present invention.
As noted above, the present apparatus preferably includes a top block. In addition, a bottom block is preferably secured to the guide so that the combination of top and bottom blocks act to confine the movement of the float on the guide. The bottom block is situated so that when the float contacts the bottom block the magnet in the float is positioned to activate the first magnetically operated switch.
A further embodiment of the apparatus involves a third magnetically operated switch located in the tubular guide a distance above the second magnetically operated switch, and preferably at substantially the same level as the alternate magnetically operated switch. This third switch is capable of being activated by the magnet in the float and is in electrical communication with the first electrical current source to cause current to flow through this switch when it is closed and part of an electrical circuit. A second relay is in electrical communication with the third switch to allow current from the second source, described previously, to provide at least one sensible (i.e., capable of being understood by the senses, such as audial, visual and the like) indication, preferably two such indications, is at least at a predetermined level upon the third switch being activated. In effect, the third switch and second relay act as an alarm system to warn that the liquid in the storage tank has built to a level predetermined to be of concern to the operator. The preferred two sensible indicators, or alarms, e.g., audial and visual, is yet another safety feature of the present invention.
When a top block is employed, it is preferably situated so that when the float contacts the top block, the magnet in the float is in position to activate the third magnetically operated switch.
Each of the first, second, alternate second and third magnetically operated switches is preferably a magnetic-reed switch. The first switch is preferably normally closed whereas the other mechanically operated switches are preferably normally open.
These and other aspects and advantages of the present invention are set forth in the following detailed description and claims, particularly when considered in conjunction with the accompanying drawings in which like parts bear like reference numerals.